Shelf



FIG. 1 is a perspective view of a shelf showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a left side view thereof.

The ornamental design for a shelf, as shown and described.